It is well known that the rate at which the heart beats is variable to enable the heart's delivery of blood to adapt to the needs of the body. Regulation of heart rate is achieved by nervous activity mediated by neural stimuli and circulating neurochemical agents. Each individual has an intrinsic heart rate level which is a function of heredity, age, sex, nervous temperament, body weight, physical condition, and health of the cardiovascular system. The heart rates occurring in periods of rest and in periods of activity varies about the intrinsic heart rate level of the individual.
It has been customary for the physician, since the beginning of recorded history, to give attention to the arterial pulse reflecting the heart beat. In general, it is customary to count the beats of the heart over a fraction of a minute and to then express the count as a minute rate. Cardiac tachometers are now available which quickly measure that minute rate.
There is a need for a device that permits correlation of heart rate with diurnal bodily rhythms, with diverse activities, and with psychological stresses. A record of heart rates occurring over a prolonged period of time such as twenty four hours or more can provide significant information regarding the state of cardiovascular health, the state of nervous tension, the action of drugs, as well as the effect of various stresses on the cardiovascular system.